The present invention relates generally to multi-channel distributed power line communication systems in general and, more specifically, to a communications terminal and an interface circuit coupled between the power line and communications terminal for providing high wide band frequency bridging impedance to communication signals present on the power line without impeding substantially the transmission and reception communication signals of the terminal.
It is generally cost prohibitive for a telephone company to service individual telephone subscribers in a sparsely populated region, like in some rural communities where the residents are separated by distances of miles. Since most, if not all, of these rural residents are equipped with power line service from a local utility, it has been proposed to provide telephone service to these subscribers by employing a frequency division multiplex telephone communication system which utilizes the power line servicing the community as the transmission carrier medium.
In some rural communities, the individual resident subscribers may be clumped together in a central location permitting their subscriber terminals to be grouped together. In this situation, the grouping of subscriber terminals may share a common power line interface, face, e.g. line tuner and line coupler pair, for bidirectional communication over the power line. Thus, the cost of an individual terminal interconnection may be kept low because the expense of the line filter and coupler pair may be allocated among the group of subscribers. However, in those rural communities where the residents are not clumped together but spread over a wide geographical area, it will be necessary to provide individual power line connections for each of the resident subscribers such as that shown in the illustration of FIG. 1.
In order for these individual power line connections (see FIG. 1) to be implemented without disrupting the transmission impedance, i.e. the impedance that an individual terminal must drive when transmitting over the power line, the individual subscriber terminals should either have a frequency selective termination, i.e. some sort of line tuner or filter, or an interface circuit which offers high bridging impedance. The cost of the power line interface circuits can no longer be shared among subscribers, but rather must be sustained by each individual subscriber. For this reason, the high bridging impedance interface circuit concept is desirable because all power line interface circuits may be made identical, rather than having a different line tuner design for each subscriber drop corresponding to the carrier frequency thereof. This, of course, will lower the cost individually of each subscriber terminal which accordingly lowers overall system costs by the number of individual terminals in the system.
To accomplish this high bridging impedance for power line interconnection, the instant application proposes an interface circuit coupled between the power line and communications terminal to provide high impedance to the carrier frequency communication signals present on the power line utilizing electronic means.